1. Field of the Invention
The present invention relates to a wire cleaning device for a corona discharge type charger installed in an image recording apparatus and, more particularly to a wire cleaning device for a corona discharge type charger such as a charger for charging a photoconductive element, a transfer charger or a separation charger which is built in an electrophotographic copier, for example.
2. Discussion of the Background
An electrophotographic copier or similar image recording apparatus which is implemented by an electrostatographic process includes a photoconductive element. Arranged around the photoconductive element are various process units including a charger for charging the surface of the photoconductive element, optics for forming a document image on the charged surface of the photoconductive element, a developing unit for developing the image on the photoconductive element by toner or similar developer, a transfer charger for transferring the resulting toner image to a paper, a separation charger for separating the paper from the photoconductive element after the image transfer, and a cleaning unit for removing toner particles remaining on the photoconductive element after the image transfer. Among such units, the chargers adapted to charge the photoconductive element are in many cases implemented by corona discharge type chargers. This type of charger is usually comprised of a shield case having an opening which extends over substantially the entire length of the surface of the photoconductive element which is to be charged, end blocks made of a dielectric material and positioned at opposite ends of the shield case, and a wire extending between the end blocks.
A problem with a charger of the type described is that its wire is often stained with grease of an operator's hands during assembly and/or gathers impurities such as toner particles, dust particles and moisture floating in the copier during copying operation. Such impurities deposited on the wire would lower the discharging efficiency of the charger and bring about irregular discharging, thereby degrading the quality of reproduction. Such an occurrence has to be eliminated by cleaning the wire occasionally. There has been proposed a wire cleaning device having cleaning members in the form of cleaner pads which are made of urethane foam or similar soft material, and a support member which is made of polycarbonate or similar insulating material for supporting the cleaner pads. To clean the wire, the support member is slidingly moved along the shield case of the charger so that impurities deposited on the wire may be removed by friction. More specifically, two cleaner pads are mounted on a support member such that they extend parallel to each other at opposite sides of the wire and in a plane perpendicular to the plane which faces the surface of the photoconductive element. In the event of cleaning, the cleaner pads are caused to slide on the wire while sandwiching the latter from opposite sides. A drawback with such a configuration is that although the impurities present in those portions of the wire on which the cleaner pads act may be removed, the impurities deposited in the portion of the wire which faces the photoconductive element and the portion which is diametrically opposite thereto cannot be removed because the friction pads do not act thereon at all. The wire therefore cannot be sufficiently cleaned of impurities and suffers from a considerable decrease in charging efficiency and irregular charging.
Another approach proposed in the light of the above noted information is to hold a single cleaner pad in contact with that portion of the wire which faces the surface of the photoconductive element to be charged, as disclosed in Japanese Laid-Open Utility Model Publication (Kokai) No. 58-146246. Such an approach, however, brings about another drawback that the wire yields during cleaning because the cleaner pad contacts the wire from one side only. Again, this prevents impurities from being sufficiently removed from the wire.
Each of the prior art cleaning devices discussed above are usually securely mounted on a body of a copier or similar image recording apparatus. Every time a charger is moved into and out of the apparatus body, the cleaner pad or pads act on the wire of the charger to remove impurities from the wire based on such movements of the charger. This is undesirable because impurities collected by the cleaner pads when the charger was pulled out of the apparatus body are apt to be deposited again on the wire when the charger is pushed into the apparatus body.